Electron discharge device



Aug. 16, 1949 w. WATROUS, JR, ET AL 2,479,529

ELECTRON DISCHARGE DEVICE Filed Nov. 23, .1945

ATTORNEY Patented Aug. 16, 1949 ELECTRON DISCHARGE DEVICE Ward W.Watrous; Jr.,

Herbert Gleason, Bloo Chatham, and Charles infield,

N. J assignors to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application November 23, 1945, SerialNo. 630,340

7 Claims.

This invention relates to electron discharge devices and moreparticularly to devices wherein an ionizable medium or atmosphere ispresent. Such devices include the so-called glow discharge tube andgaseous rectifiers and thyratrons.

In discharge devices of the character indicated, particularly in thosewherein a control electrode is employed, it is necessary to control theinitiation of the discharge. It is desirable in this type of electrondischarge devices, especially those for heavy current and voltageindustrial use, to utilize cathodes and anodes of as large a size aspracticable in order to provide for the desired'high rating for thetube. A desideratum for controlled discharge devicesof-the gaseous orvapor type, inter alla, requires that the grid potentials for controlshould be of a convenient order of magnitudeeven for tubes designed tooperateat high values of anode voltage; and also requires that the gridgeometry should be such as to minimize the tendency to surge. Surging isthe term used in the art to designate the sudden extinction of thedischarge. That extinguishing of the discharge probably is the result ofa very sudden deionization of the discharge region, Such very suddencessation of the flow of current in the circuit of which the device is apart, may induce abnormally high voltages of destructive magnitude inthe equipment associated with the tube.

We have found that for a given discharge cur- I.

rent the tendency of the tube to surge increases both with decrease ofthe open grid area through which the discharge current flows duringoperation, and with decrease of the density of the gas or vapor.

Generally speaking, the ionizable medium in a discharge device of thecharacter indicated is obtained by introducing a specific gas, of whichneon, argon, xenon and krypton are examples, into the previouslyevacuated envelope, and sealing the gas therein. Such a device is knownas a gaseous type tube distinguishing it from the vapor type of tubewhich is made by evacuating the envelope and introducing mercury, zinc,tin, or other material having sufiiciently low vapor pressure that itwill produce a vapor of that material in the device when heated. Eachtype has limitations. For instance, the high voltage gasfilled thyratronrequires a low gas density, and conventional designs which permit lowvalues of grid bias voltage, are prone to surge. On the other hand,conventional high voltage vapor type thyratrons using mercury arelimited in condensed mercury temperature operating range, because toohigh bias voltage is required at high our invention;

2 temperatures and surging occurs at low temperatures.

Broadly stated, the present invention is directed to the provision of anelectron discharge device having an ionizable medium, wherein ade-.quate ionization for starting purposes is obtained but with a limitationimposed upon the discharge path for initiation of the discharge current.

A further general object of the invention is to increase materially theoperating temperature range for a device of the character described.

Again, a general object of the invention is to provide a constructionwhich will permit reduction of gas density in a gaseous type dischargedevice.

More specially. an object of the invention is to provide an improvedcontrol electrode.

Yet another object of the invention is to pro-. vide a control electrodeconstituting a partition and said partition providing regions forcontrol of the discharge initiation and for the operating dischargefollowing initiation.

Other objects of the invention will appear to those skilled in the artto which the invention appertains as the description progresses, both bydirect recitation thereof and by implication for the context.

Referring to the accompanying drawing in which like numerals inreference indicate similar parts throughout the several views:

Fig. 1 is an elevation, with part of the envelope broken away andinternal parts shown in section, of an electron discha ge deviceembodying Fig. 2 is a cross-section taken on line 11-11 of Fig. 1; and

Fig. 3 is a perspective view of the control electrode partition.

In the specific embodiment of the invention illustrated in said drawing,the reference numeral l9 designates a sealed envelope which has beenevacuated and supplied with an ionizable medium, either as a gas such asrecited above or a vapor of a reconstructing or other vaporizable sourcesuch as mercury and analogous substances. The envelope is showncylindrical and at one end is provided with stem I l projectinglongitudinally therein for introduction of usual lead-in wires l2 for acathode l3 and lead-in wire M for a grid l5. At the opposite end of theenvelope is provided longitudinally thereof a coaxial post 16 carryingat its inner end an anode ll of carbon or other suitable material whichprovides a surface directed toward the cathode and perpendicular to theaxis of the envelope. Said post connects through the end of the envelopeto a metallic connector cap I8 at the exterior of the envelope.

The cathode I3 is here illustrated as of the corrugated ribbon type suchas described in Patent 1,968,608 of July 31, 1934, to Lowry, and mountedwith its axis perpendicular to the axis of the envelope as in priorpatent of co-inventor W. W. Watrous, Jr., herein, No. 2,254,922 ofSeptember 2, 1941 (both said patents being assigned to the same assigneeas the present invention). The ends of the ribbon constituting thecathode are welded or otherwise secured to the aforementioned lead-inwires [2 which also function as rigid supports therefor. The cathode isrendered electron emissive, as by a coating of barium, strontium and thelike, or otherwise.

Around the cathode is a shield It which is here shown of generallyfrusto-conical shape situated axially of the envelope and provided withbulges 20 in its tapered wall to afford clearance opposite the ends ofthe cathode. This shield is closed at its bottom and supported byeyelets 2! of which one is secured to one lead-in wire l2 and another toa dummy or other supporting post 22. Of course, the second lead-in wirefor the filament is electrically free from the shield to avoid a shortcircuit. The smaller end of the frusto-conical shield is shown open anddirected axially toward the anode.

The grid l5 preferably comprises, coaxial with the envelope, a hollowcylindrical shield portion 23 and a transverse partition 24 therein. Thesmaller end of the frusto-conical cathode shield [9 projects, withclearance, into one end of the cylindrical shield portion 23 of thegrid, and the anode is located, with circumferential clearance, entirelywithin the other or upper end of the shield portion of the grid.Partition 24 is a metallic disc located between said smaller end of thecathode shield and the anode. The disc has a peripheral cylindricalflange 24* which fits within and is secured to the inside cylindricalsurface of the shield. Upper end of the shield portion of the grid ispreferably closed, suitable insulated passage for the anode post Itbeing provided therethrough. The grid is supported by rods 25longitudinally thereof secured on the inside cylindrical face of theshield portion below the partition and carried by a clamp collar 28 onthe stem H.

The grid partition 24 is, for its greatest area, a solid wall fullyblockin electron or ion flow, but provides two general regions throughwhich discharge may pass. As shown, the first of these regions isprovided by a slot 21 extending in a diametric direction of thepartition and parallel to the axis of the cathode thereby locating theslot in the direct path of electron flow from cathode to anode. Thesecond region is offset from such direct path and is shown as obtainedby provision of arcuate slots 28 near the rim, or marginally of thepartition, and symmetrically situated on opposite sides of the diametricslot 21. The center of curvature for the arcuate slots is coincidentwith the center of the partition. Preferably the length of the diametricslot is not greater than the diameter of the smaller end of thefrustoconical cathode shield, whereas the diametric distance between thearcuate slots is greater than the smaller end of the cathode shield withthe slots separated by solid material of the partition greater than thewidth of the slots, and thus deviation in fiow path from cathode toanode through the 4 arcuate slots due to the described geometry isrequired.

The essential feature of the grid is accordingly satisfied in provisionof the diametric slot to constitute what we have termed above as thefirst region, and the arcuate or off-set slots to constitute the secondregion. The first region is for the purpose of controlling the dischargeinitiation and to pass a part of the discharge current. The secondregion is substantially exclusive to any initiating discharge and has aminor effect on the control of initiation, but furnishes an additionalpath for the discharge current. The influence of this second region onthe control is kept small by using a geometrical relationship betweenthe cathode, anode and this region which results in small contributionto the off-cathode field gradient as compared with the off-cathode fieldgradient resulting from the presence of the first region. By using agrid partition comprised of two such general flow-passage regions, andsolid elsewhere, sufficient discharge area through the grid may beobtained to prevent surging, while maintaining grid control potentialsof convenient magnitude even for very high potentials. It mayfurthermore be pointed out that the diametric slot 21 representing thfirst region, for controlling the initiation discharge, is much smallerthan the second region exemplified by arcuate slots 28. Said diametricslot 21, though small, obtains control with low potentials, whereasdischarge once initiated then utilizes the diametric and arcuate slotswhich offer sufficient area to prevent surging. A specific example ofdevice employing a grid partition constructed as herein shown anddescribed operated at mercury-vapor temperature of ten to fifteendegrees centigrade lower than similar devices not employing suchpartition.

We claim:

1. An electron discharge device comprising an envelope having anionizable medium, a cathode and an anode opposed one to the other, andan interposed partition between the cathode and anode, said partitionhaving separated co-planar openings therethrough each open at one faceof the partition to the cathode and at the other face of the partitionto said anode, said openings constituting discharge passage regions onefor passage of discharge inclusive of initiating discharge and the otherfor passage of discharge substantially exclusive of initiatingdischarge.

2. An electron discharge device comprising an envelope having anionizable medium, a cathode and an anode opposed one to the other, andan interposed partition between the cathode and anode, said partitionhaving an opening in direct line between the cathode and anode, andhaving another opening for discharge passage from cathode to anodeoff-set from direct line between cathode and anode.

3. An electron discharge device comprising an envelope having anioniza'ble medium, a cathode having an axial length, an anode having asurface parallel to the axis of the cathode, and a grid partitioninterposed between said cathode and said parallel anode surface, saidpartition having a slot parallel to said cathode axis and interposed indirect line between the cathode and anode, said partition having anotherslot off-set from the first said slot and out of direct line between thecathode and anode.

4. An electron discharge device comprising an envelope, a cathodetherein having an axial length, an anode opposed to said cathode, and agrid partition between the anode and C thode and parallel to the axis ofsaid cathode, said grid partition having an opening in direct linebetween the cathode and anode and having elongated arcuate openingsoffset in their entirety from direct lines between the cathode and anodeand offset from the first said opening.

5. An electron discharge device comprising an envelope, a cylindricalhollow grid shield therein, a cathode shield having one end projectinginto the grid shield, an anode at an opposite end part of the gridshield from said cathode shield, a grid partition in said grid shieldtransverse thereto and interposed between said cathode shield and anode,said grid partition having openings therethrough spaced from each otherdistances greater than the width of the openings measured on anintercepting radius of the partition, and a cathode in said cathodeshield.

6. A grid partition comprising a metallic disc having a diametric slottherein and having elongated arcuate slots therein on opposite sides ofand symmetrical with respect to said diametric slot.

7. A grid partition comprising a metallic disc having a diametric slottherein and having elongated arcuate slots therein adjacent theperiphery thereof and having the center of curvature of said arcuateslots coincident with the center of said disc.

WARD W. WATROUS, JR. CHARLES HERBERT GLEASON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS- Number Name Date 1,997,831 Mitsuda Apr. 16, 19352,121,591 Gessford et al June 21, 1938 2,144,505 Mouromtsefi' et a1.Jan. 1'7, 1939 2,175,894 Hutchings Oct. 10, 1939 2,225,645 Kuipers Dec.24, 1940 2,245,998 Pietsch June 17, 1941 FOREIGN PATENTS Number CountryDate 321,197 Great Britain Nov. 4, 1929 334,256 Great Britain Sept. 1,1930

